修复super block(ext4)

数据无价，请谨慎操作。
通常在作磁盘操作之前应该备份磁盘的数据，在作这个操作之前也应该把磁盘上的所有内容备份到另一个磁盘中。就是说如果这个故障盘是20g的话，就需要一个20G的备份空间。备份的命令如下：

#dd if=/dev/baddrive of=/storagearea

注意：首先确定设备文件系统类型

file -s /dev/sdb

[root@dhcp-0-175 ~]# dumpe2fs /dev/sdb1

dumpe2fs 1.39 (29-May-2006)

dumpe2fs: Bad magic number in super-block while trying to open /dev/sdb1

Couldn't find valid filesystem superblock.

[root@dhcp-0-175 ~]# tune2fs -l /dev/sdb1

tune2fs 1.39 (29-May-2006)

tune2fs: Bad magic number in super-block while trying to open /dev/sdb1

Couldn't find valid filesystem superblock.

根本无法从dumpe2fs和tune2fs看到Backup superblock的位置。

查看super block备份 

[root@10-4-1-38 ~]# mke2fs -n /dev/vdb

mke2fs 1.41.12 (17-May-2010)

Filesystem label=

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

Stride=0 blocks, Stripe width=0 blocks

3276800 inodes, 13107200 blocks

655360 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=4294967296

400 block groups

32768 blocks per group, 32768 fragments per group

8192 inodes per group

Superblock backups stored on blocks: 

32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 

4096000, 7962624, 11239424

上面的super block可以依次尝试修复

[root@dhcp-0-175 ~]# fsck.ext3 -b 98304 /dev/sdb1

e2fsck 1.39 (29-May-2006)

sdb1 was not cleanly unmounted, check forced.

Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure

Pass 3: Checking directory connectivity

Pass 4: Checking reference counts

Pass 5: Checking group summary information

sdb1: ***** FILE SYSTEM WAS MODIFIED *****

sdb1: 11/123648 files (9.1% non-contiguous), 8298/246991 blocks

修改完成后：

[root@dhcp-0-175 ~]# dumpe2fs /dev/sdb1

dumpe2fs 1.39 (29-May-2006)

Filesystem volume name: sdb1

Last mounted on:

Filesystem UUID: 0293bd85-b911-43bf-853e-6588b3eaaf39

Filesystem magic number: 0xEF53

Filesystem revision #: 1 (dynamic)

Filesystem features: has_journal resize_inode dir_index filetype sparse_super large_file

Default mount options: (none)

Filesystem state: clean

Errors behavior: Continue

Filesystem OS type: Linux

Inode count: 123648

Block count: 246991

Reserved block count: 12349

Free blocks: 238693

Free inodes: 123637

First block: 0

Block size: 4096

... ...
如果上述方法不行，则可以尝试如下方法，但有风险

man mkfs.ext4可以看到-S参数
-S     Write superblock and group descriptors only.  This is useful if all of the superblock and backup superblocks are  corrupted,  and  a last-ditch  recovery  method  is desired.  It causes mke2fs to reinitialize the superblock and group descriptors, while not touching the inode table and the block and inode bitmaps.  The e2fsck program should be run immediately after this option is used, and  there is  no  guarantee  that  any  data  will be salvageable.  It is critical to specify the correct filesystem blocksize when using this option, or there is no chance of recovery.

[root@dhcp-0-175 ~]# mke2fs -S /dev/sdb1

mke2fs 1.39 (29-May-2006)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

24480 inodes, 97656 blocks

4882 blocks (5.00%) reserved for the super user

First data block=1

Maximum filesystem blocks=67371008

12 block groups

8192 blocks per group, 8192 fragments per group

2040 inodes per group

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 37 mounts or

180 days, whichever comes first. Use tune2fs -c or -i to override.

[root@dhcp-0-175 ~]# mount /dev/sdb1 /mnt/

[root@dhcp-0-175 ~]# ls /mnt

foo a b